29 July 2008

This thread at an angling website has me nervous. Using Marmorkrebs as live bait seems to be a very poor idea, since the whole point is, well, to introduce the thing into a wild habitat while it's still alive. Admittedly, they're not supposed to get away, but it seems a lot easier for them to get away when they're in a lake or a river than when they're in a tank in your living room.

22 July 2008

I now have two fairly reliable reports of fish hobbyists in North America with Marmorkrebs. These two cases are quite distant from each other geographically. I am very interested in tracking the spread of these animals through the pet trade in North America.

08 July 2008

The newest issue of Current Biology has a very good primer on crustaceans in general. It contains a very brief mention of Marmorkrebs:

The recent finding of a parthenogenetic crayfish strain in the aquarium trade also poses a potential threat if it makes its way into the wild.

Unfortunately, there are no references, nor any attempt at naming the crayfish, making this perhaps a somewhat cryptic reference to a novice reader -- which is exactly who this article is directed at!

As readers of this blog will know, it is no longer an "if" as to whether Marmorkrebs makes its way into the wild. It already has done. Such is the curse of lead time (the delay between when something is written and when it appears in print).

Neurobiology is fundamentally about cellular communication. Cells communicate in several ways, but in neurons, the primary way that neurons communicate with each other across synapses. Synapses are, strictly speaking, the physical gaps between neurons, but the term is often loosely expanded include the cellular machinery to send and receive signals across that gap. If you understand synapses, you're a long way towards understanding brains and all they do.

Crayfish have made a big impact on our understanding of synapses. In 1976, Harold Atwood wrote:

The largest part of our available knowledge of the mechanisms of chemical synaptic transmission comes from work on vertebrate (especially frog) neuromuscular synapses. Probably the synapses between the giant fibers of the squid would rank second in significance, while third place would go to the neuromuscular synapses of crustaceans.

There were many reasons why the connections between neurons and muscles in crustaceans made such a big impact on our understanding of synaptic physiology. Detailing them all would take several posts, but it sort of boils down to three factors.

First, the muscle cells are huge.

Second, there are only a few neurons connecting to muscles.

Third, the connection between neurons and muscles in crayfish is not like the connection between neurons and muscles in mammals.

If you ever took a basic physiology course, you probably learned two things: that neurons only excite muscles, and that how many neurons are fired controls how much a muscle contracts. This is true for mammalian skeletal muscle, but it's not true for crustaceans.

In crustaceans, some neurons inhibit muscles, and the pattern of neurons firing plays a much bigger role in determining how much a muscle contracts. Consequently, synapses between neurons and muscles in crustaceans are much more like synapses in brains than the highly specialized synapses between neurons and muscles in mammalian skeletal muscle. Mammalian muscle synapses are, to be blunt, quite boring.

All this is preamble to the actual discovery mentioned in the title of this post.

Neurons continually communicate with each other, but they don't necessarily act on that communication. Neurons are the kings of filtering out mixed messages. Typically, a neuron receives a conflicting mess of excitatory and inhibitory signals. By adding them all up, it determines whether to fires (sending a signal to the next neuron) or not. Thus, inhibition occurs on the receiving end, which is said to be postsynaptic.

Using crayfish claw muscles, Josef Dudel and Steve Kuffler found an entirely different way that neurons can inhibit signals. Rather than sending an inhibitory signal to a neuron directly, they found one neuron could "intercept" a signal that another neuron had sent before it reached its recipient.

The "interecepting" inhibitory neuron accomplished this by releasing inhibitory neurotranmitter not onto the recipient neuron, but by releasing the inhibitory chemical onto the sender, right at the very end, just as the signal is about to release the sender's neurotransmitter.

Of course, as with all interceptions, timing matters. If the interceptor released its inhibitory signal too early (shown in A) or too late, there was little inhibition. But if the interceptor released its signal a couple of milliseconds before the sender (shown in B), it could almost entirely knock out the signal from the sender to the recipient.

This mechanism of presynaptic inhibition was later found to fairly widespread. It occurs in vertebrates, and in synapses within brains. It wasn't just a quaint little crayfish curiosity.

06 July 2008

I've talked a little about open access research publishing here, so wanted to point out the recent sniping across no man's land on the subject. The opening salvo was fired by Nature. I haven't read the article, because it's password protected and I don't want to pay the 8 bucks, so you can guess where Nature stands on this issue. The tone of the article seems to have caught many off guard as quite nasty.

The Nature article does have reader comments below it, if you have some time. There's quite a few.

You can find a compilation of reactions to the Nature article at A Blog Around the Clock, which includes this pithy comment:

...PLoS has no intention to in any official way acknowledge the existence of this article (according to the old blogospheric rule "Do Not Feed The Trolls")(.)

There's also a lengthy post over at The Questionable Authority on the subject.

My only comment for now is to repeat the mantra that led me to start this website.

Ideas that spread, win.

Additional: Greg Laden has compiled things that Nature has published about PLoS over the years here.